For optimal performance, a directional antenna such as a reflector antenna requires close alignment with a target signal source. Alignment of a reflector antenna is typically performed via an adjustable antenna mount that, with respect to a fixed mounting point, is adjustable in azimuth and elevation to orient the antenna towards the target signal source.
Distance target signal sources, such as satellites, may require alignment precision on the order of 1/100 of a degree for maximum signal efficiency.
Typical mechanized antenna pointing arrangements apply a drive motor with a position feedback loop to energize the drive motor forward and backwards along a single axis. Alignment in multiple axes is adjusted until a desired directional alignment is reached. Mechanical linkages between the drive motor and antenna base may be via gears, belts, cables, chains or the like.
A significant problem with mechanical linkage precision, especially where a high level of pointing precision is required, is backlash/hysteresis accumulated from slack in the mechanical linkage, rotational bearings, gear teeth and or gear mounting keyways.
A prior antenna pointing solution addressing the backlash/hysteresis problem applies a high precision gear drive having a large bull gear directly driven by two pinion gear drive servo motors to precisely control antenna position. The two servo motors are controlled to maintain a minimum level of torque against each other with only one servo drive at a time delivering the extra power to overcome the other servo drive and rotate the antenna to position. Thereby, all of the backlash/hysteresis in the system is preloaded to one side. However, even if manufactured with a high level of precision, there is backlash/hysteresis in the gears themselves, the keyways holding the gears to the drive shafts, in the pinion gear reduction box, in each bearing in the drive train, and even in the shafts themselves. The precision manufacturing tolerances required in a drive system of this type significantly increases costs, especially where the drive system dimensions must be scaled to point an antenna of significant size and/or under variable wind load conditions. Further, gear driven antenna pointing systems of this type add significant weight to the overall antenna system, a significant factor for mobile satellite communications systems.
Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art.